[llvm-branch-commits] [flang] [mlir] [flang][OpenMP] Lower target in_reduction for host fallback (PR #199967)

[Sairudra More via llvm-branch-commits]

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@@ -8334,6 +8393,36 @@ convertOmpTarget(Operation &opInst, llvm::IRBuilderBase &builder,
             targetOp.getPrivateNeedsBarrier(), &mappedPrivateVars)))
       return llvm::make_error<PreviouslyReportedError>();
 
+    // Map in_reduction block arguments to the per-task private storage
+    // returned by __kmpc_task_reduction_get_th_data. The lookup must run
+    // inside the target task body so the gtid corresponds to the executing
+    // thread. The descriptor argument is NULL: the runtime walks enclosing
+    // taskgroups to locate the matching task_reduction registration for
+    // `origPtr`. Mirrors the in_reduction handling on omp.taskloop.context.
+    ArrayRef<BlockArgument> inRedBlockArgs = argIface.getInReductionBlockArgs();
+    if (!inRedBlockArgs.empty()) {
+      llvm::OpenMPIRBuilder &ompB = *moduleTranslation.getOpenMPBuilder();
+      llvm::Module *m = moduleTranslation.getLLVMModule();
+      llvm::LLVMContext &llvmCtx = m->getContext();
+      uint32_t srcLocSize;
+      llvm::Constant *srcLocStr = ompB.getOrCreateDefaultSrcLocStr(srcLocSize);
+      llvm::Value *bodyIdent = ompB.getOrCreateIdent(srcLocStr, srcLocSize);
+      llvm::Function *gtidFn = ompB.getOrCreateRuntimeFunctionPtr(
+          llvm::omp::OMPRTL___kmpc_global_thread_num);
+      llvm::Value *bodyGtid =
+          builder.CreateCall(gtidFn, {bodyIdent}, "omp_global_thread_num");
+      llvm::FunctionCallee getThData = ompB.getOrCreateRuntimeFunction(
+          *m, llvm::omp::OMPRTL___kmpc_task_reduction_get_th_data);
+      llvm::Type *ptrTy = llvm::PointerType::getUnqual(llvmCtx);
+      llvm::Value *nullDesc = llvm::ConstantPointerNull::get(ptrTy);
+      for (auto [blockArg, origPtr] :
+           llvm::zip_equal(inRedBlockArgs, inRedOrigPtrs)) {
+        llvm::Value *priv = builder.CreateCall(
+            getThData, {bodyGtid, nullDesc, origPtr}, "omp.inred.priv");
+        moduleTranslation.mapValue(blockArg, priv);
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Saieiei wrote:

Agreed. If this runtime lookup path remains after the representation cleanup, I’ll move the reusable codegen part into OMPIRBuilder instead of keeping it directly in translation.

https://github.com/llvm/llvm-project/pull/199967